Neurological disorders such as seizure disorders are usually treated with medication. However, there are patients who are not helped by medication—they may not be able to tolerate the side effects or the medication itself is not efficacious for their particular disorder. This is a significant problem in that seizure disorders can be life threatening. Moreover, the quality of life for victims of severe epilepsy can be severely impacted. Neuropsychiatric disorders such as depression and ADHD are also typically treated with medications that have deleterious side effects and lack of efficacy. To offer patients relief that medication alone cannot deliver, various neurostimulation methods have been developed. For example, vagus nerve stimulation (VGS) has been shown to be therapeutically useful. Similarly, deep brain stimulation (DBS) and responsive neurostimulation (RNS) approaches are known to have efficacy. But these neurostimulation techniques are invasive as they require surgical implantation of electrodes. Thus, these techniques are relatively expensive and involve the dangers associated with the surgical implantation of the electrodes.
To provide neurostimulation without the invasive dangers of prior art techniques, an alternative neurostimulation therapy has been developed that involves trigeminal nerve stimulation (TNS). For example, a cutaneous embodiment of TNS involves the transcutaneous stimulation of the supraorbital nerves and/or the supratrochlear nerves in the forehead. Like other cranial nerves, the supraorbital and supratrochlear nerves arise through foramina in the skull. The supraorbital nerve arises from the supraorbital foramen above the orbit. Since one has two eyes, there are thus two supraorbital nerves that ascend vertically toward the scalp from their respective foramen. The supratrochlear nerve is medial with regard to the supraorbital. But it also then ascends vertically towards the hairline. There are thus two supratrochlear nerves, each arising from its respective orbit. A supraorbital nerve and supratrochlear nerve thus associates with each orbit. The forehead is thus an ideal location to stimulate the trigeminal nerve in that the supraorbital nerve and supratrochlear nerve associated with each orbit are located medially on the forehead. The skin and fascia over the forehead is relatively thin such that the supratrochlear and supraorbital nerves are readily stimulated transcutaneously.
One approach to stimulate the supratrochlear and supraorbital nerves requires a clinician to palpate for the supraorbital notch or foramen so that a suitable electrode can be applied adjacent the notch. The electrode would be sized so that it would cover not only the trunk of the supraorbital as it arises from its foramen but also the trunk of the corresponding supratrochlear nerve. To provide bilateral stimulation, the clinician would also palpate for the remaining supraorbital notch and apply another electrode accordingly. Although such an approach provides advantageous neurostimulation for treatment of disorders without invasive implantations or deleterious pharmaceutical side effects, the treatment is burdened by the need for expert application of the electrodes. For example, if a lay person applies the electrodes in this fashion and locates the electrodes too laterally on the forehead, the resulting bilateral current excited between the two electrodes may penetrate to the brain. Thus, the application of electrodes in this fashion required medical expertise, which greatly increases costs as the patient must visit a medical facility daily for chronic treatments.
To provide efficacious trigeminal neurostimulation therapy without the need for daily medical facility visits, a cutaneous electrode assembly 10 as seen in TNS system 100 of FIG. 1 supports electrodes (not illustrated) such that if a patient medially centers electrode assembly 10 across their forehead, the contained electrodes are then positioned over the supraorbital and/or supratrochlear trunks. To ensure the maximum coverage or stimulation of each supraorbital and supratrochlear nerve trunk, the patent may be instructed to align an inferior edge of electrode assembly just above their orbital arches. If electrode assembly 10 has electrodes configured for bilateral stimulation of the trigeminal, one or more electrodes will thus be on located above each orbit and over the supraorbital notches such that a pulse transmitted between the electrical contacts for each orbit will conducts across the supraorbital and supratrochlear nerve fibers as they arise from their respective orbits. Moreover, these nerve branches are relatively shallow with regard to the forehead skin surface and thus readily stimulated by electrode assembly 10.
A patient can easily apply electrode assembly 10 in the correct position by centering it across the forehead median. Although electrode assembly 10 has conductive gel so as to adhere to the forehead, a retainer device 24 may also be used to help secure electrode assembly 10. A pulse generator 15 drives electrode assembly 10 through a cable 20. It is important that a patient be able to correctly position a TNS electrode so that the appropriate nerves are stimulated without the risks of current penetration to the brain. Because a patient can readily position electrode assembly 10 medially on their forehead using a landmark such as their nasal midline, the patient needs no knowledge of anatomy in that regard yet they are positioning the electrode in an advantageous location for TNS therapy. Studies have shown that TNS carried out in this fashion are significantly more efficacious than the use of conventional VNS. Yet TNS is far less invasive, has much fewer risks, and considerably lower cost than VNS.
Although TNS is thus an attractive alternative to VNS, problems remain with regard to it use. For example, it is conventional in the cutaneous electrode arts to use a conductive gel to adhere an electrode to the skin. The gel is quite sticky and serves as both an adhesive and an electrical conductor. It is thus conventional to apply EEG and EKG electrodes using conductive gel. Similarly, conductive gel is used to apply TENS (transcutaneous electrical nerve stimulation) electrodes. But such applications are relatively temporary. In contrast, the electrical stimulation from TNS may need to be applied for hours at a time such as while sleeping or even 24 hours a day. The forehead is a problematic environment for such long-term adhesion as the forehead skin is generally quite oily. Moreover, the excessive oil tends to make the forehead more prone to contaminates such as dust or dirt. An electrode applied with conductive gel to the forehead will thus tend to come off during such relatively-long periods of time. This is problematic as the electrode can only provide therapy while it is attached to the patient. Moreover, the peeling off of the electrode can induce arcing from the electrode to the patient. Accordingly, there is a need in the art for improved TNS electrodes.